I was going to say bullshit when the demon girl said there were humans on the base of this being a scifi story, the human race is exclusive to Earth, is almost totally impossible for another planet to have something even close to us, lucky planet.
But the explanation for it was splendid, same for the translation device working, the new people inherited and changed the original language but not so much to make it impossible for the super computer to understand.
I'm guessing that Noah will found out the truth after discovering some old ruins or special made bunker his mother left explaining everything.